1. Field of the Invention
The present invention relates to a quantity adjusting apparatus that adjusts a volume of an audio signal and quantities such as the number of minutes and the number of seconds of time.
2. Description of the Related Art
There is a quantity adjusting apparatus that adjusts quantities such as a volume of an audio signal and the number of minutes and the number of seconds of time by an operation performed by a user through an operating section. A volume adjusting apparatus that adjusts a volume of an audio signal is provided to various apparatuses that generate audio such as AV equipment including a stereo unit and a television set, and a personal computer. A conventional volume adjusting apparatus includes a volume knob for instructing a volume of an audio signal, a rotary encoder for outputting a pulse according to an operating speed of the volume knob, a microcomputer for determining a volume of an audio signal, and an electronic volume for changing a volume of an audio signal based on the volume of the audio signal determined by the microcomputer. The rotary encoder is rotatable together with the volume knob, and outputs a pulse every time it rotates a predetermined angle so as to output a pulse according to an operating speed (rotational angular velocity) of the volume knob. The microcomputer determines a new volume every time a pulse is output from the rotary encoder. For example, the microcomputer determines, as a new volume, a volume obtained by adding 2 dB to a current volume every time a pulse is output. Then, the electronic volume changes a volume of an audio signal into a new volume determined by the microcomputer. Whether the volume is increased or decreased, that is, in which direction the volume knob is turned can be determined by comparing two kinds of pulses having different phases which are output from the rotary encoder.
In the conventional volume adjusting apparatus, the number of pulses has a directly proportional relationship with the increase/decrease of the volume. For this reason, for example, when a volume is set to be increased/decreased by 1 dB with respect to one pulse, that is, when a change in the volume with respect to one pulse is set small, a user needs to greatly turn the volume knob in order to greatly change the volume. On the contrary, for example, when the volume is set to be increased/decreased by 4 dB with respect to one pulse, that is, when the change in the volume with respect to one pulse is set large, it is difficult for the user to finely adjust the volume. The conventional volume adjusting apparatus is not easy for the user to handle.
A volume adjusting apparatus described in Japanese Patent No. 3654064 determines a new volume, every time a pulse is output (a pulse period is measured), based on a pulse interval (period) that is an interval between output start times of two pulses and a current volume. Specifically, a new volume is determined according to a function represented by the following equation (1). Herein, V represents a current volume, Tp represents a pulse interval, a, b, c, and d represent constants larger than 0.|f(V,Tp)|=a/(Tp+b)(V+c)+d  (1)When the volume is determined according to the equation (1), an absolute value |f(V,Tp)| of the volume is inversely proportional to a pulse interval Tp. For this reason, when the volume knob is turned slowly, the pulse interval Tp output from the rotary encoder becomes large, and thus a variation of the absolute value |f(V,Tp)| of the volume becomes small. Further, since the time interval at which the volume is changed becomes longer, the user can easily and finely adjust the volume by turning the volume knob slowly. On the contrary, when the volume knob is turned fast, the pulse interval Tp output from the rotary encoder becomes small, and thus the variation of the absolute value |f(V,Tp)| of the volume becomes large. Further, since the time interval at which the volume is changed is shortened, the user can easily and greatly change the volume by turning the volume knob fast. Thus, the volume adjusting apparatus described in Japanese Patent No. 3654064 is easier for the user to handle than the above conventional volume adjusting apparatus.
As described above, the volume adjusting apparatus described in Japanese Patent No. 3654064 determines a new volume based on a pulse interval and a current volume every time a pulse is output. However, when a process of determining a new volume is performed every time a pulse is output, this process for determining a new volume disturbs processes other than the process for adjusting the volume by the microcomputer (for example, operation control of AV equipment having the volume adjusting apparatus). Therefore, in order to reduce the load of the microcomputer, it is considered to count the number of pulses within predetermined time, measure the pulse interval, and perform the calculation based on the equation (1) the same number of times as the counted number of pulses after lapse of the predetermined time, so as to determine a new volume. However, in this case, when the number of pulses counted within the predetermined time is two or more, the time interval between output starting times of two pulses cannot be properly measured, and a false volume might be determined according to the equation (1). In some cases, the time intervals of every volume determining process performed by the microcomputer are varied according to the load on the microcomputer. For example, when the load on the microcomputer is small, the time interval of the volume determining process is shortened, whereas when the load on the microcomputer is large, the time interval of the volume determining process is lengthened. Particularly, when the load on the microcomputer is large and the time interval of the volume determining process performed by the microcomputer is lengthened, the number of pulses counted within the predetermined time becomes large. For this reason, it is highly unlikely that the time interval of the output starting times of two pulses is properly measured, and a false volume is more likely to be determined. When the false volume is determined and a volume of an audio signal is changed by the electronic volume, the change in the volume gives the user a feeling of strangeness.